Snap action element



Jan. 18,1944.

H. D. MATTHEWS SNAP ACTION ELEMENT Filed Aug. 3, 1942 IN VEN TOR.IEowarl. 'D. Mal thew Patented Jan. 18, 1944 UNITED STATES PATENT OFFICESNAP ACTION ELEMENT Howard D. Matthews, Detroit, M.ich., assignor toMinneapolis-Honeywell Regulator Company, Minneapolis, Minn., acorporation of Delaware Application August 3, 1942 Serial No. 453,354

8 Claims. (01. 297-15) and also add greatly to the expense ofmanufacture. It is therefore the main object of the present invention todesign a thermostatic snap action device which does not depend for itssnap action on the operation of an external spring or toggle mechanism;

Another object of the invention is to form a bimetallic strip in suchmanner that the end portions thereof are bent backward upon themselveswith the two extreme ends normally overlapping each other, and then toprovide some means for preventin the overlapping of the two ends so thatstresses are set up in the bimetallic strip. These and other objectswill readily become apparent as the following specification is read inthe light or the accompanying drawing, the single figure'of whichillustrates one embodiment of my invention. I i Referring now. to thedrawing, a supporting bracket l may be suitably fixed to an insulatingpanel H, the upper portion 01' the bracket Ill having a forwardlyextending portion l2. which suitably carries an intermediate portion l3of the bimetallic thermostatic strip generally indicated at I. Thetwoend portions! 5 are looped around and bent back upon themselves in sucha manner that if unrestrained they would overlap each other. Instead ofbeing unrestrained, however, they are separated and the two extreme endsare seated in oppositely disposed notches IT in the operating member H!which slides vertically through openings in the two forwardly extendingportions l9 and carried by the bracket l0. Adjustable screw 22 passe'sthrough an opening in the intermediate portion l3 of the bimetallicstrip l4 andis screw threaded into the forward extension I 2 to form anadjustable stop for the operating member is.

A second bracket 23 is suitably fixed to insulating panel II andcarries'a second adjustable screw 24 which is screw threaded in aforwardly member l8 are thus determined by the adjustment of the twoscrews Hand 24.

With the parts, in the position shown in the drawing, .the two endportions ii of the Strip It will tend to move the operating member 18 inan upwardly direction against the adjustable screw 22 due to" the factthat these end portions I5 are biased towards each other by reason ofthe inherent resilience of the strip and by being further forciblyseparated by the operating member i8. Assuming that the active elementof the bimetal is on the inside, then an increase in temperature willbuild up a force in the bimetal tending to cause the ends I5 to deflectdownwardly. At first this force will be opposed by the aforementionedstress in the bimetal tending to hold the element [8 against the screw22, but after a suificient change in temperature the force in thebimetal which is due to the increase in temperature will overcome theforce due to the stress in the bimetal and cause the ends IE to start tomove the operating member l8 downwardly. As soon as the member l8 startsto move downwardly the angle at which the ends l5 apply their force tothe operating member l8, will be decreased and this angle, as well asthe spring rate of the bimetal, is so chosen that as soon as theoperating member l8 starts to move the spring rate of the bimetal willbe over compensate'd so that the operating member I8 will actually snapdownwardly into engagement with the adjustable screw 24. Upon a.subsequent decrease in temperature, the opposite operation will takeplace so that as the operating member 18 is "raisedby the bimetal theangle at which the ends l5 exert their force upon the operating memberi8 is increased to again overcompensate the spring rate of the bimetaland cause the operating member thermostatic snap action mechanismutilizing a bimetallic thermostatic strip in which the snap action isdue to the stresses set upwithin the bimetal itself but which is not of'the over center" v type of snap action of the bimetal and which doesextending portion 25 on the bracket 23 to form a second adjustable stopfor the operating member l8. The limits of movement of operating notneed any extraneous element such as toggle members or springs to producethe snap action. It will also be noted that the entire snap actionmechanism is formed of active bimetal thus decreasing the operatingdifferential of the device.

The specific embodiment has been disclosed for the purposes ofillustration only and I intend to claims.

I claim my invention: 1. A device of the character described comprisingin combination, a bimetallic thermostatic trip having an intermediateportion and two end portions, said end portions being bent back uponthemselves and located opposite each other, said end portions furtherbeing biased toward each other by reason of the inherent resilience ofthe strip, and movable means located between said end and forcing themapart thereby setting up stresses in said strip, said two endsdeflecting in the same direction with a snap action upon changes intemperature.

2. A device of the character described comprising in combination, abimetallic thermostatic strip having an intermediate portion and two endportions, said end portions being bent back upon themselves in suchmanner that they would normally overlap each other by reason of theinherent resilience of the strip, said ends being prevented fromoverlapping whereby stresses are set up in said strip, said two endsdeflecting in the same direction upon changes in temperature, and beingso directed that upon movement of said two ends in one direction theymove with a snap action through a predetermined range.

3. A device of the character describedc'omprising in combination, abimetallic thermostatic strip having an intermediate portion and two endportions, said end portions being bent back upon themselves and towardsaid intermediate portion,

said end portions further being biased toward each other by reason ofthe inherent resilience of the strip, and movable means located betweensaid ends and forcing them apart thereby setting up stresses in saidstrip, said ends acting on said movable means at such an angle as totend to force said movable means towards said intermediate portion, a,change in temperature causing said ends to deflect away from saidintermediate portion, the resultant reduction in said angle causing suchmovement to occur with a snap action.

4. A device of the character described comprising in combination, abimetallic thermostatic strip having an intermediate portion and two endportions, said end portions being bent back upon themselves in suchmanner that they would normally overlap and extend toward saidintermediate portion, said ends being prevented from overlapping wherebystresses are set up in said, strip causing said ends to oppose eachother at such an angle that they are forced toward said intermediateportion, a change in temperature causing said ends to deflect away fromsaid intermediate portion, the resultant reduction in said angle causingthe spring rate of the bimetallic strip to be overcompensated therebycausing such movement to occur with a snap action.

5. A device of the character described comprising in combination,abimetallic thermostatic strip having an intermediate portion and twoend portions, said end portions being bent back upon themselves andtoward said intermediate portion, and movable means located between saidends and forcing them apart thereby setting up I stresses in said strip,said ends acting on said movable means at such an angle as to tend toforce said movable means towards said intermediate portion, a change intemperature causing said ends to deflect away from said intermediateportion, the resultant reduction in said angle causing the spring rateof the bimetallic strip to be overcompensated thereby causing suchmovement to occur with a snap action, and adjustable means for limitingthe amount of movement of said movable means.

6. A device of the character described comprising in combination, abimetallic thermostatic strip having an intermediate portion and'two endportions, said end portions being bent back upon themselves in suchmanner that they would normally' overlap and extend toward saidintermesuch an angle that they are forced toward saidintermediateportion, a change in temperature causing said ends to deflect away fromsaid intermediate portion, the resultant reduction in said angle causingthe spring rate of the bimetallic strip to be overcompensated therebycausing such movement to occur with a snap action, and means forindividually adjusting the amount of travel of said ends in eachdirection.

7. A device of the character described com prising in combination, abimetallic thermostatic strip having an intermediate portion and two endportions, said end portions being bent back upon themselves and. beingbiased towards each other because of the inherent resilience of thestrip and being located opposite each other, and movable means locatedbetween said ends and forcing them apart thereby setting up stresses insaid strip, said two ends deflecting in the same direction with a snapaction upon changes in temperature, and means for guiding said movablemeans for straight line movement.

8. A device of the character described comprising in combination, abimetallic thermostatic strip having an intermediate portion and two endportions, said end portions being bent back upon themselves and towardsaid intermediate portion, and movable means located between said endsand forcing them apart thereby setting up stresses in said strip, saidends acting on said movable means at such an angle as to tend to forcesaid movable means towards said intermediate portion, a suflicientchange in temperature to start said ends to deflect away from saidintermediate portion, the resultant reduction in said angle causing thespring rate of the bimetallic strip to be overcompensated therebycausing such movement to'be completed with a snap action, and means forguiding said movable means for straight line movement.

HOWARD D. MATTHEWS.

